This study will seek to understand the structural requirements necessary for hallucinogenic and stimulant activity in phenethylamines. It will initially focus on a group of closely related amphetamine analogs of well known pharmacological properties. Physical-chemical and biochemical parameters believed to be important in hallucinogenic and stimulant activity will be measured. Correlations will then be made with hallucinogenic potency. Special attention will be given to distinguishing "psychotomimetic" from stimulant activity.